Anencephaly: causes, symptoms and prevention

Neural tube defects are alterations that occur during the first weeks of fetal development and that cause malformations of varying severity. While some of them are incompatible with life, others can cause only mild paralysis.

The case of anencephaly is particularly severe; brain it is not fully formed, so babies with this disorder do not live long. Let's see what they are symptoms and causes of anencephaly and how this defect can be prevented.

• Related article: "Macrocephaly: causes, symptoms and treatment"

What is anencephaly?

Anencephaly is also known as "open-skull aprosencephaly." It is a developmental disorder of the neural tube that causes serious disturbances in the growth of the fetus.

In anencephaly the brain and skull do not develop as expectedrather, they do so incompletely. This causes babies with anencephaly to be born without large regions of the brain, without some bones. of the head and without portions of the scalp, for which the brain is partially discovered.

This alteration occurs in approximately 1 in every thousand pregnancies; However, since most of the time the life of the fetus ends in a spontaneous abortion, the number of babies with anencephaly that are born is 1 in every 10,000 newborns. It is more common in girls than in boys.

The defects caused by anencephaly are extremely severe and prevent the baby from living. Most of the affected children die a few hours or days after birth, although there have been cases of children with anencephaly who have lived to almost 4 years.

Anencephaly can be total or partial. It is considered to be partial when the roof of the skull, the optic vesicles, and the back of the brain are developed to some degree, while if these regions are absent we speak of anencephaly total.

Symptoms and signs

In babies affected by anencephaly, the telencephalon, which contains the cortex and therefore the cerebral hemispheres, is usually absent; the same is true of the skull, meninges, and skin. In its place is usually a thin layer of membrane.

Consequently, anencephaly makes the baby unable to carry out basic functions or superior, how to feel pain, hear, see, move, feel emotions, or think, even though in some cases they can emit reflex responses. This means that the little ones with this alteration never become aware of their environment.

In addition to these signs and symptoms, abnormalities in the face and heart defects are common. The alterations are more marked the greater the missing part of the brain and skull.

The diagnosis of anencephaly can be made during pregnancy through different procedures. Ultrasound can reveal the presence of polyhydramnios (excess amniotic fluid), while amniocentesis can detect elevated levels of alpha-fetoprotein.

Causes of this alteration

Anencephaly occurs as a result of a neural tube evolution defect which normally occurs in the fourth week of embryonic development. The neural tube is the structure that gives rise to the central nervous system, that is, the brain and the spinal cord. In this particular case, the tube does not close at its rostral or superior end.

There are other alterations that are due to an abnormal development of the neural tube; collectively they are known as "neural tube defects", and in addition to anencephaly include spina bifida, in which the spinal column closes incompletely, and Chiari malformations, which cause brain tissue to spread to the spinal canal.

The fact that the neural tube does not close properly causes the amniotic fluid that protects the fetus comes into contact with the nervous system, damaging neural tissue and preventing normal brain development and of cerebellum, and therefore causing deficits or even the absence of the functions associated with them.

Genetic and environmental risk factors

Normally the appearance of this defect does not depend on heredity but on a combination of genetic and environmental factors. However, some cases have been detected in which anencephaly has occurred repeatedly in the same family, and having a baby with anencephaly increases the risk of it also occurring in successive pregnancies.

The specific hereditary mechanism by which this happens is not known, although it is believed that there is a relationship between anencephaly and the MTHFR gene, involved in the processing of the vitamin B9, also known as folic acid or folate. Alterations in this gene appear to increase the risk of anencephaly, although not very significantly.

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Environmental risk factors that affect the mother are probably more relevant than genetic ones. Among these types of factors, scientific research highlights the following:

• Vitamin B9 deficiency.
• Obesity.
• Mellitus diabetes, especially if it is type I and is not controlled.
• Exposure to elevated temperatures (eg. and. fever, saunas).
• Consume of anti-seizure medications such as lamotrigine.

It also appears that anencephaly is more common in babies born to Asian, African and Hispanic mothers, although it is not known why this increased risk is due.

Treatment and prevention

Anencephaly can't be cured. Normally, babies born with this problem are given food and water and care is taken to ensure that are comfortable, but use of medication, surgery, or assisted breathing is considered to be Irrelevant; since the little one will never acquire consciousness, they are usually allowed to die naturally, without being artificially resuscitated.

Research has shown that intake of folic acid (vitamin B9) greatly reduces the risk of neural tube defects, including anencephaly and spina bifida. This vitamin is found both in foods, for example green leafy vegetables, and in dietary supplements; in this second case, 0.4 mg daily seems to be sufficient.

However, the intake of vitamin B9 must be done before pregnancy, since these alterations are produced normally during the first phase of fetal development, before the woman detects that she is pregnant. Thus, specialists recommend increasing the consumption of this vitamin when you start trying to have a baby.